The neuropeptide, gonadotropin-releasing hormone (GnRH) plays a primary role in the development of the reproductive system and in the subsequent regulation of reproductive function in adults. Although it is generally supposed that the GnRH neurons of primates are homogenous and that they secrete only one molecular form of the decapeptide, we now have strong evidence to indicate that both of these assumptions are incorrect. In this pilot study we aim to refine our preliminary observations by demonstrating that GnRH in the rhesus macaque hypothalamus is encoded by two distinct genes (GnRH-I and GnRH-II), and that both the GnRH-I and GnRH-II neurons exist as many anatomically and biochemically distinct sub-populations. Specifically, we propose to: (1) Use Dil and Fluoro-Gold tracing to determine which of the novel GnRH neuronal sub-populations send axons to the median eminence and, by inference, contribute to the neuroendocrine control of the reproductive axis; (2) Use in situ hybridization (ISH) and RT-PCR to determine whether the expression of GnRH-I and GnRH-II mRNA changes significantly during prepubertal development; our preliminary data suggest that different GnRH neuronal sub-populations are associated with different aspects of maturation; (3) Produce monoclonal antibodies specific to GnRH-II and its associated peptide (GAP-II); these will be used for radioimmunoassay, immunocytochemistry (ICC), and for future immunoneutralization studies; (4) Use confocal microscopy to determine which GnRH neuronal sub-populations express glutamate receptors of the NMDA sub-type, thereby paving the way for selective ablation of these neurons through stereotaxically administered excitotoxins; our preliminary data already show that different GnRH neuronal sub-populations differ markedly in their capacity to express GluR1 (an AMPA glutamate receptor sub-unit); (5) Use ICC and ISH (for GnRH-I and GnRH-II) to examine changes in the GnRH neuronal system of female macaques during key reproductive events, such as the preovulatory luteinizing hormone surge. Taken together, the results are expected to revolutionize our current ideas about the neuroendocrine mechanisms controlling reproductive function in primates. Moreover, they should help to lay a foundation for novel approaches to contraception and for the development of therapies for centrally-originating human reproductive disorders, such as precocious and delayed puberty, and amenorrhea.